Not quite. If you blow positive on the road-side machine they arrest you and take you to the nick. You are then breathalysed again with one of these
. If that is STILL positive then you are charged with the offence and then normally bailed to appear in court. If it's negative then you are given a bit of a lecture and then told to bugger off and don't do it again.
The result of the machine at the station IS recognised by the court so that's enough to get you banned.
There has been challenges to this in the UK but the UK Judiciary isn't quite a flexible as US courts so the chances of that defense working are pretty well zero unless the coppers cocked up and didn't calibrate the machine that night or something.
As for the blood sample, the police will ask if you want to have one taken so it can be checked [you can have a sample as well]. You don't have do but it's worth doing as it just MIGHT get you off the hook if the result is borderline.
Here in Oz they have Booze Buses where they block the road and breathalyse whoever they feel like. If you blow positive they have everything nicely ready in the bus including the accurate machine etc. ready for customers - and they LOVE doing it at 8:30 in the morning also.